The present invention relates to a cleaning system used in semiconductor fabrication processes. More particularly, it relates to a system for cleaning a semiconductor wafer which makes a drainage of a cleaning liquid more efficient.
In line with the progress in operations for manufacturing semiconductor devices using high integration technology, particulate dust remaining on the surface of a wafer adversely affects the characteristics of the semiconductor devices. Accordingly, a better technique for cleaning semiconductor wafers by which particulate dust can be removed from the surface of the wafers is needed in the semiconductor fabrication processes.
Semiconductor devices having a pattern size of about 0.5 .mu.m are now mass-produced, using the current ultra large-scale integration technology, and the process for fabricating such microscopic devices requires a dust-free production environment, not to mention surface treatment and cleaning techniques. In particular, according to the trend toward increasing the wafer size and decreasing the chip size, continuous researches have been devoted to develop a bath system using a wet process.
The following description with reference to the attached drawings relates to a conventional wafer cleaning technique.
FIGS. 1A and 1B are schematic views of a conventional system for cleaning semiconductor wafers.
FIG. 1A depicts an overflowing bath system including an internal cleaning tank 1 having an intake 3 through which a cleaning solution is supplied toward the center of the lower section thereof, an external cleaning tank 2 designed to enclose the internal cleaning tank 1 and having an outlet 4 used to release the used cleaning solution to a space separated from the internal cleaning tank 1, and a circulating pipe 10 through which the outlet 4 is connected to the intake 3. The overflowing bath system also includes a circulating pump 5 formed in the middle section of the circulating pipe 10 and used to circulate the cleaning solution repeatedly, and a filter 6 which percolates or filters the cleaning solution repeatedly circulated by the circulating pump 5 and returns the filtered cleaning solution to the internal cleaning tank 1 through the intake 3.
The operation of the overflowing bath system is described as follows.
The operation of the overflowing bath system begins with passing the cleaning solution through the filter 6 using the circulating pump 5. The cleaning solution is then provided to the internal cleaning tank 1 through the intake 3. Wafers 8 mounted on a cassette 7 are then soaked in the cleaning solution. Particulate dust adhered to the surfaces of the wafers 8 is removed by the cleaning solution circulating between the wafers 8.
That is, cleaning and etching processes are performed by the movement of cleaning solution and chemical reaction between the cleaning solution and the wafers 8.
When the cleaning solution starts to overflow after completely filling the internal cleaning tank 1, the cleaning solution passes through the outlet 4 of the external cleaning tank 2 and is filtered through the filter 6 by the circulating pump 5. The cleaning solution percolated by the filter 6 then returns to the internal cleaning tank 1 wherein the wafers 8 are mounted. After that, the cleaning solution may circulate repeatedly or may be dumped into a waste barrel based on a predetermined standard. In other words, when the circulating pump 5 is driven, a waste valve 11 is closed, and when the cleaning solution is to be dumped into a waste barrel, the waste valve 11 is opened to release the used cleaning solution to outside.
FIG. 1B depicts a downflowing bath system including an internal cleaning tank 100 having an outlet 40 used to release the used cleaning solution through the center lower section thereof, an external cleaning tank 200 designed to contain the internal cleaning tank 100 and having an intake 300 through which a cleaning solution is supplied to a space separated from the internal cleaning tank 100, and a circulating pipe 101 through which the outlet 40 is connected to the intake 300. The downflowing bath system also includes a circulating pump 50 formed in the middle section of the circulating pipe 101 and used to circulate the cleaning solution repeatedly, a filter 60 which filters the cleaning solution circulated by the circulating pump 50 and returns the filtered cleaning solution to the internal cleaning tank 100 through the intake 300, and a baffle plate 90 formed in the lower section of the internal cleaning tank 100 for separating a cassette 70 containing wafers 80 from the bottom of the internal cleaning tank 100.
The operation of the downflowing bath system is described as follows.
The operation of the downflowing bath system begins with passing the cleaning solution through the filter 60 using the circulating pump 50. The cleaning solution is then provided to the internal cleaning tank 100 through the intake 300. The cleaning solution flows into the tank 100 from the above and fills the tank 100. The cassette 70 containing the wafers 80 is fixed to the baffle plate 90 of the internal cleaning tank 100, and is soaked in the cleaning solution. The wafers 80 mounted on the cassette 70 are washed by the circulating cleaning solution. Then the cleaning solution passes through the baffle plate 90 and is percolated through the filter 60. The percolated cleaning solution is continuously circulated by the circulating pump 50. When the circulating pump 50 of the downflowing bath system is driven, a waste valve 51 is closed, and when the used cleaning solution is to be dumped into a waste barrel according to a predetermined standard, the waste valve 51 is opened to release the used cleaning solution to outside.
Such conventional cleaning systems have the following disadvantageous aspects.
According to the overflowing bath system having the intake in the lower section of the internal cleaning tank, the cleaning solution flows upwardly which causes the particulate dust remaining on the portions of the cassette supporting the wafers to migrate upwardly. Thus, the dust may again spread over the frontside or backside of the wafers or cause a chemical reaction to contaminate the surfaces of the wafers, because such a contamination source (e.g., the particulate dust) is positioned near the intake and the cleaning solution passes through the intake and then the contamination source to reach the wafers.
On the other hand, in the downflowing bath system, since the cleaning solution streams substantially straight, the contaminant dust is not completely removed from the portions of the wafers supported by the cassette, but is spread among the wafers during the cleaning process to migrate to the frontside or backside of the wafers or to the baffle plate. Therefore, it is difficult to effectively and completely remove the dust contaminating the surfaces of the wafers by using the above-mentioned conventional cleaning systems.
Moreover, if subsequent processes are carried out, such a condition where the cleaning process for the wafers is imperfectly performed deteriorates processing efficiency and the characteristics of semiconductor devices.